Salt-induced ordering in lamellar colloids

Uncharged rods and disks have long been known to exhibit an isotropic to nematic phase transition on increasing density. In aqueous solution, however, such particles are generally highly charged, leading to repulsive electrostatic interactions. In this article the effect of adding salt to a monodisperse solution of thin charged colloidal disks is examined. The addition of microscopic salt ions more efficiently screens the largely quadrupolar electrostatic repulsion between the mesoscopic colloidal particles, while at the same time the electric double layer around each disk contracts. By treating each disk with its associated double layer as a new effective particle, the role of salt on the phase diagram of dilute suspensions is investigated.